Localization of carboxyl groups at surface layer of carboxylated polymer emulsion particles by alkali treatment

Abstract

For the purpose of localizing carboxyl groups from inside to particle surface, styrene — butyl acrylate — methacrylic acid (74.3/17.0/8.7, mol ratio) terpolymer emulsion was kept under pH 9 at different temperatures. The amount of carboxyl groups at the particle surface, As, was remarkably increased by the alkali-treatment above 35 °C. On the other hand, As value of the alkalitreated emulsion was decreased by keeping under ph 3 above 45 °C, although in the case of the original emulsion without the alkalitreatment, it was not changed by the acid-treatment. These results suggest that a part of polymer segments which have ionized carboxyl groups is dragged out at the surface by an increase in the affinity of the groups against water, and the dragged segments turn back into the inside again when the carboxyl groups are deionized.